1. Field of the Invention.
The present invention relates to an open liquid surface cover and, more particularly, to a highly efficient and economical float for substantially reducing evaporation and heat loss from an open liquid surface.
2. Description of the Prior Art.
May industries make use of open process tanks or utilize large open liquid surfaces. While a complete list of industrial activities utilizing open process tanks would be extensive, some of the more common examples are tanks used for plating, anodizing, acid pickling, dying, rinsing, phosphating, food processing, chemical treatment, galvanizing, degreasing, and the like. Other industrial applications utilize large liquid surfaces, such as in sewage treatment plants, waste oil pits, and the like.
Since it is essential in most of these applications to have unimpeded access to the liquid in the tank, the top of the tanks must remain open. However, this creates a wide variety of problems. Since such tanks are generally maintained at elevated temperatures, the most serious problems are those resulting from evaporation and heat loss. In addition, these tanks frequently produce unpleasant vapors which may be a hazard to health and corrode surrounding structures and equipment. Additional problems result from splashing of the liquid when various components are dipped into and removed from the tank and freezing of the liquid in cold weather.
The initial steps to overcome these problems were to use extractor fans to remove the vapors from a plant and to utilize protective clothing for the operators. However, these measures never got to the root of the problem, i.e. providing a cover for the open liquid surface.
Accordingly, the search for solutions to this problem has centered around developing a method which combines the heat conserving advantages of a solid lid and the easy accessibility of an open liquid surface. One proposed method is to cover the surface with a layer of oil, such as paraffin. However, the paraffin acts as an impurity, risking contamination of the liquid. The use of oil also represents a considerable fire hazard in many applications.
Another proposed solution is to use a foaming agent on the surface of the liquid. However, it is difficult to control the foam cover so that this process is expensive and the agent requires continual replenishment. While other surface agents have been proposed, they also present problems in control, require continual replenishment, and may interfere with the industrial process.
The most effective and simple solution to the problem of evaporation and heat loss and removal of fumes and odor has been to cover the surface of a liquid with a layer or blanket of floating objects of various shapes and sizes. For example, in German Pat. No. 1,060,323 a plurality of hollow, floating bodies are provided which have a foam structure incorporating a plurality of cavities, along with raised portions and trough-like depressions. However, these bodies suffer in two major respects. Due to their irregular shape, a substantial amount of evaporation losses are still present. Also, when the bodies are initially fed to the surface of the liquid, they tend to pile up upon one another rather than orienting themselves to cover the complete liquid surface. Also, when various components are removed from the tank, the bodies are displaced and move on to the top of adjacent bodies to form a pile, thus leaving a hole in the covering.
The most common body for use in these circumstances is a hollow sphere. A single layer of balls spread across the surface of a liquid will cover approximately 91 percent of the surface, thereby eliminating many of the disadvantages mentioned previously. When spheres are initially fed to the surface of the liquid, they readily orient themselves to cover the liquid surface. When components are inserted into and removed from the tank, the bodies readily reorient themselves. Thus, balls reduce evaporation, cut heat losses, substantially reduce fumes and odor, stop splashing, improve safety, and virtually eliminate contamination. The use of balls is less costly than various types of hinged lids in that the ball surface can be broken by an object immersed into the liquid and will reform to cover it.
On the other hand, several problems still remain with the use of hollow or solid spheres. For example, spheres rotate on the surface of the liquid so that the rotating ball carries some of the liquid above the cover of spheres. As a result, a substantial amount of evaporation still occurs. One proposed solution to this problem is disclosed in U.S. Pat. No. 3,401,818 which contemplates preventing the rotation of such spheres by the use of a circular bead of uniform thickness and radial width, the width and the weight of the bead being such that the spheres are prevented from rotating on the liquid. Another approach is to use a triangular-shaped fin extending radially outwardly to form a weight which prevents rotation of the spheres. While this reduces evaporation, the method still suffers from the fact that one layer of balls covers only approximately 91 percent of the liquid surface. Thus, 9 percent of the surface is still open for evaporation and heat loss and in many applications this is unacceptable. Accordingly, it is common to use one or more additional layers of balls in an attempt to substantially cover the surface. However, this is simply not possible with spheres, which do not nest in a manner which permits a substantially complete cover.